Accelerometers may be used in activity trackers which monitor the physical activity of the users who carry them. Activity may be reported to the user in a variety of units including steps taken, distance traveled, or calories burned. The units of activity may be derived from the accelerometer data using various computational algorithms. The information from activity trackers can be useful in understanding the activity patterns of users and may motivate them to higher activity levels.
Accelerometers generate readings representing acceleration. These readings can accumulate into large quantities of data. Data storage capacity on activity trackers is limited. Furthermore, some time periods generate more useful data than others. For example, periods of activity may contain more useful information than periods of inactivity. Selecting and storing data only from more pertinent time periods may allow data storage to be used more efficiently than indiscriminately storing all data. For some applications, it may be advantageous to store data from a time period when there is a high probability that the user is walking, running, or otherwise taking steps. However, step activity may be difficult to distinguish from other types of motion.